94 



REVISION OF AMERICAN MOLES— TRVE. 



skin but remains covered by that portion of the primary surface which formed the 

 bottoms of the {jrooves and which has so increased in extent that rt this stajje the 

 surface is entirely and uniformly covered by ectoderm. No traces are left either on 

 the surface or in the corium of the extensive excision which has taken place. 



The ])riucipal details of the process are readily seen on examining a section of 

 the snout, such as is rei)reseuted in fig. 38. In this figure I have drawn, with 

 the aid of camera outlines and with diagrammatic shading, a transverse section 

 of that part of the nose of a young Condj/hira indicated by the line r, fig. 37. The 

 following is a short account of the most important histological details of the proc- 

 ess. The entire circumference of the section is bounded by a thin layer of 

 epidermal cells e, beneath which all the formative processes take place. In the 

 stage of development represented in fig. 38, this layer only loosely covers the snout 

 in the region of the papilla; and later is entirely cast ofl': but it remains in inti- 

 mate connection with the remaining surface and functions as the true epidermal 

 layer, as at/. The letters op designate respectively the epidermis of the tentacnlif- 



erous area and that of 

 the sense rays. The 

 rays are embedded in 

 a layer of fibrous tis- 

 sue, which, however, 

 does not entirely cover 

 the outer surface of 

 the ray. 



Sections of the ray 

 present a crenate mar- 

 gin owing to their pas- 

 sage thnmgh the nu- 

 merous tactile papillic 

 which cover the sur- 

 face of the ray ; there 

 are three sharply 

 marked concentric 

 layer.s of tissue to be 

 ol)served in each : An 

 outer, coruificd layer 

 of the epidermis, the 

 deeper M a 1 p i g h i a n 

 layer, and a central 

 rod of connective tis- 

 sue within which the 

 nerves and blood ves- 

 sels are embedded. 

 There are no traces 



of hair follicles, sebaceous or sweat glands to be seen on the tentacles, but they 

 occur in the proximal half of the teutaculiferous area, and only make theii' appear- 

 ance on the surface of the snout after the tentacles have assumed their erect con- 

 dition. At t and h are seen the hair follicles with the young hairs. The corium 

 is an extensive layer tilling all the space between the epidermis and the nasal car- 

 tilage. The small muscles of this part of the face appear to be eutirel5' embedded 

 within this layer.' 



TBANSVEKSE SECTION OF SNOUT OF YOUNG CONDYLURA. 



(Enlarged.) 

 o= arteries; /* = ridge-like retnnauls of the primitive ectoderm seen iu section; ftz=:bonndary 

 line between Kete MalpighJi and corium; en ^ nostrils ; e=rcornified layer of the epidermis; 

 j7^ cartilaginous tissue; A = hair follicle and accessory gland ; A*=nasal cartilage; m^nasal 

 muscles ; n = nerve supplying the mucous membrane of the nose ; o ^ the future outer surface of 

 the Bnout; 7' = papilla;; r=r tactile ray, the line points to the central connective tissue con, 

 through which the blood vessels and nerves pass ; t-^ vein. 



>0n the Structure and Development of the Nasal Rays in Condylura cristata, 

 H. Ayres. Biolug. Ceutralblatt, IV, 1885, pp. 356-360. 



By i 



